The present invention relates to a magnetic recording-reproducing apparatus used in auxiliary storage of computers, and magnetic heads for use therewith, and more particularly to a superhigh recording density magnetic recording-reproducing apparatus and magnetic heads suitable for magnetic recording and reproduction with a narrow recording track.
For example, magnetic discs of a current commercially available magnetic recording-reproducing apparatus have a linear recording density of about 25 kBPI, a track density of about 1.5 kTPI and an area recording density of about 35 Mb/in.sup.2. The magnetic heads used for these magnetic discs are inductive thin film heads. One such head records and reproduces an information signal. As the recording density increases further, however, it is difficult for a single inductive thin film head to sufficiently record data and to sufficiently reproduce the recording data from a standpoint of a head structure. Thus, it seems that the use of a composite magnetic head which separately includes a recording magnetic head and a reproducing magnetic head will be required in the magnetic recording-reproducing apparatus in the future.
Known conventional composite magnetic heads use the reproducing head of a magnetoresistive (MR) type using a soft-magnetic thin film magnetoresistive effect, as disclosed in Japanese Patent Publication JP-A-51-44917. Other conventional MR heads are ones where the direction 5 of a sense current which flows through the MR element and the direction of the signal magnetic field from a medium are normal to each other, as disclosed, for example, in IEEE Trans Magnetics, Vol. MAG-7, No. 1, March 1971, pp. 150-154. Japanese Laid-Open Patent Publication (JP-A)50-65211 discloses an MR head of the type which includes two juxtaposed such MR elements with bias magnetic fields which are generated from current magnetic fields produced by currents flowing through both the MR elements and differentially amplify the output voltages from both the MR elements. Japanese Laid-Open Patent Publication (JP-A)-52-143811 discloses an MR head where the direction of the sense current flowing through the MR element and the direction of the signal magnetic field from a medium are parallel and electrodes are formed on a medium facing surface and an opposite surface of the MR film. Japanese Laid-Open Patent Publications (JP-A)61-182620 and 62-234218 disclose an MR head where the direction of the sense current flowing through an MR element and the direction of the signal magnetic field from a medium are parallel and where two MR films are connected electrically in parallel to use magnetic fields produced by currents flowing through both the MR films in the same direction to form a single magnetic domain in the MR films, and to reduce Barkhausen noise.
As described above, if the recording density in the magnetic recording reproducing apparatus increases further in the future, a composite magnetic head which includes separate magnetic heads for recording and reproduction only will be required. Even if the conventional composite magnetic head disclosed in Japanese Patent Publication JP-A-51-44917 uses the above described conventional MR head techniques, these techniques have the following problems Thus, it cannot realize a superhigh recording density magnetic recording-reproducing apparatus which provides an area recording density of 300 Mb/in.sup.2 or more.
The differential amplification type MR head disclosed in the above Publication JP-A-50-65211 is influenced by a signal magnetic field from the adjacent track because the medium facing edge of the MR film is considerably large in width compared to the track to thereby increase noise. Since it takes different times for the two superimposed MR films to absorb the signal magnetic fields, the output waveform obtained by differentially amplifying the outputs from the MR elements is greatly distorted disadvantageously. The MR heads disclosed in Japanese Patent Publications JP-A-61-182620 and 62-234218 have MR films which are connected electrically in parallel with electrodes being provided on the medium facing surface side of the MR film which is most sensitive to the signal magnetic field, so that the intensity of the resulting output signal corresponding to the signal magnetic field is low or noise due to temperature fluctuations cannot be removed. Thus, the signal to noise ratio is reduced further as the track width becomes narrower.
It is an object of the present invention to provide a superhigh recording density magnetic recording-reproducing apparatus which solves the above problems and a magnetic head suitable for recording and reproducing with narrow tracks.